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Mysterious hydrogen-free Supernova sheds light on the violent deaths of massive stars

Yellow supergiant in a dense binary with a blue, main sequence accompanying star

The artist’s impression of a yellow supergiant in a dense binary with a blue, accompanying star in the main sequence, similar to the properties derived for the 2019yvr ancestral system in Kilpatrick et al. (2021). If the ancestor system for 2019yvr was in such a binary, it must have had a very close interaction that removed a large amount of hydrogen from the yellow supergiant in the last 100 years before it exploded like a supernova. Credit: Kavli IPMU / Aya Tsuboi

A curious yellow pre-supernova star has prompted astrophysicists to reconsider what is possible with our universe’s most massive stars. The team describes the peculiar star and its resulting supernova in a new study published recently in Monthly announcements from the Royal Astronomical Society.

At the end of their lives, cool yellow stars are typically wrapped in hydrogen, which hides the star’s warm, blue interior. But this yellow star, located 35 million light-years from Earth in the Virgo galaxy cluster, mysteriously lacked this crucial layer of hydrogen at the time of the explosion.

“We have not seen this scenario before,” said Charles Kilpatrick, postdoctoral fellow at Northwestern University‘s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), which led the study. “If a star explodes without hydrogen, it must be extremely blue – really, really hot. It is almost impossible for a star to be so cool without having hydrogen in the outer layer. We looked at every single star model that could explain a star like this, and every single model requires the star to have hydrogen, which we from its supernova know it did not have. It extends what is physically possible. ”

Kilpatrick is also a member of the Young Supernova Experiment, which uses the Pan-STARRS telescope in Haleakalā, Hawaii to capture supernovae just after they explode. After the Young Supernova Experiment discovered supernova 2019yvr in the relatively nearby spiral galaxy NGC 4666, the team used deep space images taken by NASA’s Hubble Space Telescope, which fortunately already observed this part of the sky two and a half years before the star exploded.

“What massive stars do just before they explode is a big unsolved mystery,” Kilpatrick said. “It’s rare to see this kind of star just before it explodes in a supernova.”

The Hubble images show the source of the supernova, a massive star depicted just a few years before the explosion. Several months after the explosion, however, Kilpatrick and his team discovered that the material pushed out in the star’s last explosion appeared to collide with a large mass of hydrogen. This led the team to assume that the ancestor star might have exhibited hydrogen within a few years prior to its death.

“Astronomers suspect stars are undergoing violent eruptions or deaths in the years before we see supernovae,” Kilpatrick said. “This star’s discovery provides some of the most direct evidence ever found that stars experience catastrophic eruptions that cause them to lose mass before an explosion. If the star had these eruptions, it probably expelled its hydrogen several decades before it exploded. ”

In the new study, Kilpatrick’s team also presents another possibility: A less massive companion star could have removed hydrogen from the supernova’s ancestor. However, the team will not be able to search for the accompanying star until the brightness of the supernova disappears, which could take up to a decade.

“Unlike its normal behavior right after it exploded, the hydrogen interaction revealed that it’s kind of this oddball supernova,” Kilpatrick said. “But it is unusual that we were able to find its ancestor in Hubble data. In four or five years, I think we will be able to learn more about what happened. ”

Reference: “A Cool and Inflated Candidate for Type Ib Supernova 2019yvr 2.6 Years Before Explosion” by Charles D Kilpatrick, Maria R Drout, Katie Auchettl, Georgios Dimitriadis, Ryan J Foley, David O Jones, Lindsay DeMarchi, K Decker French, Christa Gall, Jens Hjorth, Wynn V Jacobson-Galán, Raffaella Margutti, Anthony L Piro, Enrico Ramirez-Ruiz, Armin Rest and César Rojas-Bravo, March 30, 2021, Monthly announcements from the Royal Astronomical Society.
DOI: 10.1093 / mnras / stab838

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